1. Field of the Invention
The invention relates to a device for the processing of a data base which is composed of a sequence of data records. This device has
a first input for successively receiving said data records from a background memory;
a comparison device for comparing a predetermined data field of a data record received with reference information and for forming a result signal on the basis of the comparison; and
an output device which has a first output, under control of a "correct" result signal, for making the relevant data record available for further processing.
1. Description of the Prior Art A device of this kind is described in U.S. Pat. No. 3,848,235. Large data bases are stored in background memories. These memories are generally of the sequential type, such as magnetic or optical disk memories or magnetic bubble memories. A data base of this kind usually consists of tables. Each element of a table is formed by such a data record which contains a number of data relating to the same entity. The entire may be, for example, a person. The information can be searched in various ways, it being assumed that all data records in the table have at the most a predetermined length:
1. selection: the entire content of a data record is or is not supplied to a user, depending on a part of its content.
2. projection: depending on a part of the content of a data record, a second predetermined part of the data record is supplied to a user.
The testing of the content in the comparison device may concern correspondence between a key word and a predetermined part of the data record to be searched. Similarly, it may concern correspondence to one of a set of key words. In the latter case, the key words are comparatively short. The projection can be performed in two or more steps; the part extracted from the content of a data record can subsequently be used as a new key word in a second table (or the same table). Finally, the content may also be tested to indicate a relationship such as "larger than", "between given limits", and different relationships can also be tested by the same comparison operation; for example: for a first field of the data record searched, correspondence is required and the value of a second field must be between predetermined limits.
The searching of the relevant information is performed by a central processor unit CPU in the known system (for example, see the abstract of said patent. This means that this unit is not available for other purposes during this period. Furthermore, in many cases the background memory supplies the information at a rate which is higher than the processing rate of the processor. Many successive access operations for the background memory are then required for the searching of a table. It is alternatively possible to transfer a block of information from the background memory to a foreground memory, but it has been found that such a foreground memory often requires a considerable capacity.